1. Field of the Invention
The present invention relates to a tape recorder which can switch the tape speed.
2. Description of the Prior Art
This kind of tape recorder includes a recording circuit having the construction shown in FIG. 1. That is, an oscillation block OSCB is connected to a magnetic head HD. In the oscillation block OSCB one end of a primary winding of an oscillation transformer T is connected to a base of a transistor Tr through a resistor R.sub.1, and the other end of the primary winding is connected to a collector of the same transistor Tr. The transistor Tr also has an emitter connected to ground. A capacitor C.sub.1, is connected between both terminals of a secondary winding of the oscillation transformer T, and one end of the parallel combination of the secondary winding and the capacitor is connected to the head HD and the other end thereof is connected to the emitter of the transistor tr through a capacitor C.sub.2.
A center tap of the primary winding of the oscillation transformer T is connected to a power supply source (not shown) through a bias resistance BR. The bias resistance BR is composed of resistors R.sub.2 and R.sub.3. When the tape speed is 1.2 cm/sec the resistance R.sub.2 is only used, and when the tape speed is 2.4 cm/sec, a parallel combination of the resistance R.sub.2 and the resistance R.sub.3 is used, so as to generate the optimum AC bias from the oscillation block OSCB. The switching of the resistances R.sub.2 and R.sub.3 in this case is carried out by a switch SW.sub.2 interlocked with a motor speed switch SW.sub.1 of a motor circuit MT.
The oscillation block OSCB is connected to an output terminal of a final stage amplifier AMP through an equalizing circuit EQ. The equalizing circuit EQ consists of a parallel combination of a resistance R.sub.4 and a capacitor C.sub.3 and a resistance R.sub.5 directly connected thereto and sets at a certain constant.
With such construction, the optimum AC bias for a tape speed can be obtained, and in this state, a recording output of the amplifier AMP is supplied to the head HD through the equalizing circuit EQ, and the recording is carried out.
However, in such a construction, since a circuit constant of the equalizing circuit EQ is made constant, when the tape speed is 1.2 cm/sec and 2.4 cm/sec, the frequency characteristic becomes different, particularly when the tape speed is 2.4 cm/sec, the frequency characteristic is extended to a higher zone to produce a strain in a high tone, and as a result, the tone quality is disadvantageously different as compared with the case of 1.2 cm/sec.
Therefore, in accordance with the tape speed, the circuit constant of the equalizing circuit is switched for the purpose of making the tone quality uniform. However, an extra switch is required, and if this switch is further interlocked with the above switches SW.sub.1 and SW.sub.2, the switch construction becomes large.
This fact is unfavorable particularly for a super-miniature tape recorder in which parts should be minimized.